Liquid dispensing method and apparatus

ABSTRACT

A method of dispensing a liquid, which handles a minimum amount of liquid without wasting it and to dispense and spray an exact amount of the liquid without precipitating solid particles. The method including the steps of regulating a flow rate of liquid in a flow passage by orifices  8 - 1, 8 - 2  while letting the liquid flow through flow passages  10 - 1  and  10 - 2  between syringes  5 - 1  and  5 - 2  by applying a pressure of 0.001 MPa to 10 MPa to liquid  6  including solid particles and filled in one syringe vessel  5 - 1  and by setting a pressure of liquid in the other syringe  5 - 2  at a lower level than the pressure of liquid in the syringe  5 - 1  and dispensing the liquid from the flow passage by an auto dispensing valve  1.

TECHNICAL FIELD

The present invention relates to a method and apparatus for dispensing aliquid such as an adhesive or a coating material including solidparticles.

BACKGROUND ART

Heretofore, a liquid such as a coating material including solidparticles has been handled and dispensed from a dispensing valve by thefollowing three methods because the solid particles easily precipitate.Note that, the expression “dispensing a liquid” as used hereincomprehends both dispensing (dispensing the liquid as it is) andspraying (spraying the liquid, that is, atomizing it and then dispensingit).

(1) A method in which a liquid stirred by a large-sized apparatus in astorage tank is divided and stored in syringes or small vessels and usedright away.

(2) A method as proposed by JP 63-119877 A, in which a liquid in one oftwo pressure vessels is pressurized with compressed air, the air of theother vessel is opened to move the liquid through a liquid flow passagebetween the two vessels, and an auto dispensing valve as a dispensingvalve is provided at an intermediate portion of the flow passage todispense the liquid while the liquid is moving. This operation iscarried out alternately between the vessels to prevent the precipitationof the solid particles.

(3) A method in which a circulation circuit is formed from, for example,a pump dispensing port to an auto dispensing valve and a pump suctionport by using a pump or the like to circulate a liquid forcedly to aportion near the needle and valve seat of the auto dispensing valve. Forexample, a dispersion (dispersion type liquid including solid particles)of a mixture of carbon particles and a binder solution which is spraycoated on the inner surface of an alkali dry battery to improve itsperformance is circulated at a relatively high liquid pressure in orderto re-disperse secondary agglomerates of the particles. Since stablecoating can be performed by employing this method while preventing theprecipitation of the carbon particles, it is globally used.

However, in the method mentioned in the above item (1), in the case of aliquid having a low viscosity in the range of 3,000 mPa·s or less,particularly about 1 to 500 mPa·s, the precipitation of the solidparticles, although depending on the specific gravity and size of theparticles, is so fast that there is a big difference between the qualityof the liquid at the start of dispensation and the quality of the liquidduring dispensation or at the end of dispensation, and particularly thecontent of the particles is the major concern. Further, the precipitatedparticles accumulate on a portion near the valve and the valve seat ofthe auto-dispensing valve, often causing a dispensation failure.

In the method mentioned in the above item (2), the flow rate of theliquid is determined by the level of air pressure. Therefore, control ofa period of time before the subsequent step, that is, from the time whenthe liquid moves from the first tank to the second tank to the time whenthe liquid moves from the second tank to the first tank is affected onlyby the pressure of compressed air. Therefore, when a commerciallyavailable air regulator is used, a low-viscosity liquid filled in asyringe having a small capacity of about 5×10⁻⁶ m³ to 30×10⁻⁶ m³ (5 ccto 30 cc) for instance, is moved to a syringe on the opposite sideinstantaneously, in less than 1 second when pressurized at a pressure of0.05 MPa which is the minimum graduation. Thereby, problems arise thatthe operation of dispensing the liquid by the dispensing valve cannot becontinued for a desired period of time and dispensation cannot becarried out stably. The method also involves problems such as theinclusion of air and the difficulty of dispensing a predetermined amountof the liquid stably.

Further, even if an air regulator equipped with a gauge having a minimumgraduation of 0.001 MPa is used to apply pressure to the liquid, themoving time of the liquid in the syringe having a capacity of 30×10⁻⁶ m³(30 cc) is in the order of second and the moving direction must bechanged frequently to carry out an automatic operation. Also, thefrequent interruption of work cannot be avoided even when a large vesselhaving a capacity of several liters is used.

Thus, to prevent the interruption of work at the time of changing of themoving direction, as proposed in JP 60-5251 A, there is a method inwhich three coating material tanks are used for the stable supply of apowder slurry coating material. In this method, pressurized air issupplied to the first tank to always maintain a fixed pressure, and thepowder slurry coating material is pumped to the third tank through acoating gun at the same liquid pressure as the pressure of thepressurized air. When the level of the first tank lowers, pressurizedair is supplied to the second tank to pump the coating material throughthe second tank and dispense it from the coating gun. In this method,while pumping from the second tank is being stabilized, 10 seconds ofsimultaneous pumping from the first and second tanks is required.

In general, these tanks have a capacity of 18×10⁻³ m³ to 30×10⁻³ m³ (18liters to 30 liters). Therefore, this method is not suitable for theabove-mentioned syringes, which are small vessels.

Further, the above-mentioned two methods disclosed by JP 63-119877 A andJP 60-5251 A involve a problem that a coating film adhered to the wallof a tank is dried upon its contact with a dry gas as the level of thecoating material lowers because a pressure source is a gas such ascompressed air. Since the powder slurry and the dispersion contain asolution of a polymer such as a binder in addition to inorganic ororganic solid particles, after they are dried, the polymer solutioncomponent which has not been re-dissolved is no better than a foreignmatter.

Furthermore, it is known in the industry that when compressed gas suchas compressed air comes into contact with a low-viscosity liquid richwith a solvent in particular, a part of the gas dissolves in the liquid.Therefore, a quality problem often occurs because micro-bubbles arecontained in the dispensed liquid.

In the method mentioned in the above item (3), a special plunger pumpwhich is free from pulses and the accumulation or agglomeration ofparticles in the circuit and which is not worn down by solid particlesmust be used. This apparatus is large in size and expensive and alsorequires one (1) gallon (about 3.8×10⁻³ m³ (3.8 liters)) or more of acoating material for stable circulation. Therefore, it is not suitableas a tester for testing with several 10×10⁻⁶ m³ (several tens of cc) ofa coating material which is required for the laboratory-leveldevelopment of a material, and a huge amount of money has been spent onthe development of a material. In addition, a large amount of a solventhas been required for the cleaning of the inside of the circuit at theend of work and most of the coating material in the circuit cannot beused because it contains a cleaning solvent.

In the past several years, the number of expensive materials has beengrowing due to progress in the development of functional coatingmaterials. Such materials include a dispersion containing inorganicparticles having a uniform particle size distribution and a size ofseveral micrometers or less, or of a nanometric level in some cases, apowder slurry containing polymer particles uniform in particle size, anelectrode-ink for the electrodes of fuel cells as proposed in U.S. Pat.No. 5,415,888 B and the like, and an electrode-ink having super fineparticles of platinum in a nanometric order carried on a carbonnanotube. Some of those coating materials not uncommmonly cost severalmillion yen per kilogram, and an apparatus and method, which not onlyallow for high-quality coating but also are capable of making the mostof a minimum amount of a coating material, are desired.

DISCLOSURE OF THE INVENTION

The present invention has been made in view of the above-mentionedproblems, and an object thereof is to provide a method and apparatus fordispensing a liquid, which make it possible to handle a minimum amountof a liquid without wasting it and to dispense and spray an exact amountof the liquid without precipitating solid particles.

To solve the above-mentioned problems, the present invention providesthe following method and apparatus for dispensing a liquid.

That is, the above-mentioned object has been achieved by providing: aliquid dispensing method including the steps of regulating a flow rateof liquid in a flow passage by flow rate regulating means while lettingthe liquid flow through the flow passage between two or more vessels byapplying a pressure of 0.001 MPa to 10 MPa to the liquid including solidparticles and filled in at least one vessel of the two or more vesselsand by setting a pressure of liquid in at least one remaining vessel ata lower level than the pressure of liquid in the at least one vessel,and dispensing the liquid from the flow passage by a valve; and anapparatus for carrying out the method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a liquid dispensing apparatusaccording to a first embodiment of the present invention used in amethod of dispensing a liquid according to the present invention.

FIG. 2 is a system diagram showing a liquid dispensing apparatusaccording to another embodiment of the present invention.

FIG. 3 is a system diagram of a liquid dispensing apparatus having threevessels according to still another embodiment of the present invention.

FIG. 4 is a time chart showing three vessels of the liquid dispensingapparatus shown in FIG. 3 illustrating in time series the relationshipamong liquid flows from the respective vessels.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be describedhereinbelow with reference to the accompanying drawings.

FIG. 1 shows a liquid dispensing apparatus DA according to a firstembodiment of the present invention used in a liquid dispensing methodaccording to the present invention. In FIG. 1, reference numeral 1denotes an auto-dispensing valve as a liquid dispensing valve. Theauto-dispensing valve 1 is connected to syringes denoted by referencenumerals 5-1 and 5-2 serving as vessels by connecting pipes 10-1 and10-2 as liquid flow passages. The syringes 5-1 and 5-2 are filled with aliquid including solid particles denoted by reference numeral 6 (forexample, solid particles having a particle diameter of a nanometriclevel to several hundreds of microns, preferably a nanometric level toseveral tens of microns are used).

Adaptors (lids) 11-1 and 11-2 are attached to the upper ends of thesyringes 5-1 and 5-2 to seal them and are connected to the feed pipes ofcompressed air as a compressed gas from air supplies, and the compressedair feed pipes are provided with regulators with relief 14-1 and 14-2and three-way solenoid valves 13-1 and 13-2, respectively, in order ofmention from the upstream thereof. Owing to this constitution,compressed air is supplied into the syringe 5-1 through the three-waysolenoid valve 13-1 while its-pressure is maintained at a predeterminedpressure by the regulator with relief 14-1 to apply pressure to theliquid 6 filled in the syringe 5-1 and pump it to the syringe 5-2through pipes 10-1 and 10-2 serving as flow passages by pressure. Atthis point, the syringe 5-2 is opened to the atmosphere by the three-waysolenoid valve 13-2 to exhaust air in a space above the liquid.

The pressure in the syringe 5-2 may be set to a desired pressure lowerthan the compressed air in the syringe 5-1 by the regulator with relief14-2 to produce a pressure difference so that the liquid can move.

As for movement, that is, inflow and outflow of the liquid from onevessel to the other, since a smooth flow can be formed when the liquidflows out and prevention of the precipitation of solid particles by ajet stream can be expected more as the pressure difference increaseswhen the liquid flows in, it is preferred that the liquid flows out andflows in from the bottoms of the vessels, that is, from the bottoms ofthe syringes 5-1 and 5-2 as in this embodiment.

Orifices 8-1 and 8-2 serving as flow rate restricting members which areone of the flow rate regulating means are provided between theauto-dispensing valve 1 and the syringes 5-1 and 5-2. The diameters andlengths of the orifices 8-1 and 8-2 are not particularly limited but maybe changed according to the viscosity and liquid pressure of the liquidor the diameter of the solid particles. In the case of a liquid having aviscosity of 3,000 mPa·s or less and including solid particles whichprecipitate relatively quickly, the orifices preferably have a diameterof 0.1 to 0.8 mm and a length of 0.5 to 10 mm, thereby making itpossible to control the moving time of 30×10⁻⁶ m³ (30 cc) of the liquidhaving a viscosity of 100 mPa·s and a faster precipitation speed at aliquid pressure of 0.01 MPa in the range of 1 to 10 minutes.

The flow rate restricting members are not limited to a particular shapeand may be needle valves whose openings can be adjusted. It is alsopossible to use processed injection needles having a small diameter, orannealed stainless steel tubes having a desired length and an innerdiameter of, for example, 1.59 mm ( 1/16 inch). Further, after the flowrate restricting members divide the flow into a plurality of narrowpaths, the divided flows may be impinged with one another and used inconjunction with means for dispersing agglomerates of solid particles tocarry out excellent impingement dispersion.

At the upstreams of the orifices 8-1 and 8-2 serving as flow raterestricting members, screens 9-1 and 9-2 serving as filters areprovided. The screens 9-1 and 9-2 are used to prevent dry foreignmatter, which has adhered to the walls of the syringes serving as thevessels and fallen off from the wall, from flowing down. That is, theforeign matter is prevented from blocking the orifices 8-1 and 8-2serving as flow rate restricting members and from mixing into thedispensed liquid.

In the liquid dispensing apparatus DA constituted as described above,foreign matter is removed from the liquid including the solid particlesby the screens 9-1 and 9-2 in the pipes 10-1 and 10-2 serving as flowpassages from the syringe 5-1 to the syringe 5-2, and the liquid ispumped in a direction shown by solid line arrows “a” in FIG. 1 in theabove-mentioned predetermined moving time of 1 to 10 minutes while theflow rate of the liquid is regulated, to the above-mentionedpredetermined value by the orifices 8-1 and 8-2. Pressurized air issupplied from an air supply to a piston 2 connected to a needle 3 of theauto-dispensing valve 1 attached between the pipes 10-1 and 10-2 througha three-way solenoid valve 12 to lift up the needle 3 against thepressure force of a spring CS. A clearance is formed between the needle3 and a valve seat 4, and the liquid including solid particles isthereby dispensed from an opening in the valve seat 4. When the liquidlevel of the syringe 5-1 lowers and reaches a low level or the liquidlevel of the syringe 5-2 reaches a high level, the supply of compressedair by the three-way solenoid valve 13-1 attached to the upper adaptor11-1 of the syringe 5-1 is cut off, and compressed air begins to besupplied through the three-way solenoid valve 13-2 attached to the upperadaptor 11-2 of the syringe 5-2 while it is maintained at apredetermined pressure by the regulator with relief 14-2. As a result,the liquid 6 in the syringe 5-2 is pressurized and pumped in a directionshown by double-dotted line arrows “b” in FIG. 1 in the pipes 10-2 and10-1 serving as flow passages to flow into the syringe 5-1. At thispoint, the syringe 5-1 is opened to the atmosphere by the three-waysolenoid valve 13-1 to exhaust air in the space above the liquid. Whenthe liquid level of the syringe 5-2 lowers or reaches a low level or theliquid level of the syringe 5-1 reaches a high level, the flowingdirection of the liquid is switched alternately between the syringes 5-1and 5-2 in the same manner as described above to carry out dispensingoperation continuously.

Thus, in the embodiment shown in FIG. 1, since the liquid includingsolid particles is pumped in the flow passages 10-1 and 10-2 asdescribed above, the precipitation of the solid particles is preventedand the flow rate of the liquid is regulated by the function of theorifices 8-1 and 8-2 to make the liquid flow through the flow passagesat a predetermined velocity. Therefore, a liquid having high quality anduniform dispersibility of the particles is dispensed by theauto-dispensing valve 1 for a desired period of time. Thus, smoothcontinuous operation is carried out. Therefore, when the syringes 5-1and 5-2 are vessels having a small capacity of about 5×10⁻⁶ m³ to30×10⁻⁶ m³ (5 to 30 cc) for instance, and an expensive liquid is filledinto the syringes to be dispensed, this method is particularly usefulbecause a minimum and exact amount of the liquid can be dispensedwithout wasting it.

Note that, in the embodiment shown in FIG. 1, the vessels are shown assyringes 5-1 and 5-2. However, in the present invention, the shape andsize of the vessels are not particularly limited. When the vessels areused at a low pressure, commercially available inexpensive plasticsyringes as shown in the above-mentioned embodiment having a capacity of5×10⁻⁶ m³ to several 100×10⁻⁶ m³ (5 to several hundred cc) may be used.Also, commercially available inexpensive pots having a capacity of about1×10⁻³ m³ (several liters) may be used. When a relatively high liquidpressure is desired, a three-piece structure consisting of a pressureresistant hollow metal cylinder or tube as a barrel portion, an upperportion and a bottom portion may also be used.

In the present invention, the flow rate regulating means can be used tomove the liquid intermittently (discontinuously). That is, as shown inFIG. 1, compressed air supplies connected to the adaptors 11-1 and 11-2of the syringes 5-1 and 5-2 are opened and closed intermittently(discontinuously) by the three-way solenoid valves 13-1 and 13-2 toapply pressure to the liquid intermittently so as to move it regularlywith regular pulses. Note that, the liquid may be dispensed from thedispensing valve 1 while a stable liquid pressure between pulses isbeing maintained.

Also, in the present invention, as shown by chain lines in FIG. 1,plungers denoted by reference numerals 7-1 and 7-2 may be installedbetween the liquid 6 in the syringes and the compressed gas. Theplungers 7-1 and 7-2 can prevent the dissolution of the gas in theliquid because they separate the liquid from the compressed gas. Inaddition, the plungers 7-1 and 7-2 may have the same diameter as theinner diameter of the syringes 5-1 and 5-2 to achieve the same pressureas the compressed gas. The ratio of the liquid pressure can be changedby varying the diameter of unshown cylinders using pistons connected tothe plungers 7-1 and 7-2. The ratio of the sectional area of each of theplungers 7-1 and 7-2 to the sectional area of each of the cylinders orthe pistons is called “pump ratio” in the industry. When the cylindersare smaller than the plungers 7-1 and 7-2, the liquid pressure becomeslower than the pressure of the compressed gas and when the cylinders arelarger than the plungers 7-1 and 7-2, the liquid pressure becomes higherthan the pressure of the compressed gas.

That is, in the present invention, by setting the ratio to 1/10, aliquid pressure of 0.001 MPa can be easily obtained with a compressedgas pressure of 0.01 MPa and by setting the ratio to 20, a liquidpressure of 10 MPa can be obtained at a normal compressor air pressureof 0.5 MPa in a production plant. For example, the low pressure in theformer case is suitable for double-fluid spray whereas the relativelyhigh liquid pressure of up to about 10 MPa in the latter case issuitable for airless spray.

In the present invention, as proposed in JP 2-111478 A, a pressuredevice having a pump ratio of 20 may be used to apply a liquid pressureof 10 MPa, for instance, so as to bring a liquefied carbonic acid gasinto a super critical state so that the gas is mixed with ahigh-viscosity liquid to obtain a low-viscosity fluid. Even in the caseof a low-viscosity liquid, it can be mixed with a liquefied carbonicacid gas which has been brought into a super critical state and sprayedto form a dry film, by making use of the property of the liquid that itvolatilizes instantaneously when it is sprayed. In the presentinvention, the pressure and temperature of the carbonic acid gas are notparticularly limited as far as it is in a range where it does not departfrom the super critical state. For example, the gas can move the fluidwhile maintaining a differential pressure of about 10 MPa and atemperature of about 50° C.

Further, in the present invention, the liquid can be moved in accordancewith an electric plunger type volumetric method by combining a plungerwith a servo motor or stepping motor instead of using the compressedgas. In this method, there is a merit in that even a material whoseviscosity increases with the elapse of time like a reactive type liquid,in particular, can be moved in a predetermined amount of the materialper unit time and can be dispensed in a predetermined amount of thematerial.

Still further, in the present invention, the amount of the liquid equalto the amount dispensed by the auto-dispensing valve 1 can be suppliedautomatically or regularly into the vessel or circuit by an unshownseparate liquid feeder at a higher pressure.

Furthermore, in the present invention, the liquid can be dispensed whileit is moved. In the case of a liquid having no quality problem and a notso high precipitation speed, an unshown on-off valve provided among avessel pressurized by once stopping the movement of the liquid in theflow passages 10-1 and 10-2 for a desired period of time, for example,another vessel at a downstream of the syringe 5-1 in FIG. 1 and, forexample, a portion of the connection position with the pipe at the lowerend of the syringe 5-2, that is, at an upstream of the syringe 5-2 maybe closed to dispense the liquid. While the movement of the liquid inthe flow passages 10-1 and 10-2 is once suspended by making thepressures of the two or more connected vessels the same, the liquid canbe dispensed from the auto dispensing valve 1.

In addition, in the present invention, a solvent may be mixed into thecompressed gas to prevent a liquid film adhered to the inner walls ofthe vessels from being dried, and as shown by chain lines in FIG. 1, asolvent S may be collected in depressions R formed on the gas side ofthe plungers 7-1 and 7-2 to create a solvent saturated atmosphere.

In the present invention, the liquid dispensed from the auto-dispensingvalve 1 may be filled into other small-sized vessels etc., alone or as afiller. It may also be applied to an object to be coated and its form isnot particularly limited.

Further, in the present invention, the liquid can be sprayed byattaching a spray nozzle to the distal end of the auto-dispensing valve1. The sprayed liquid particles may be used for granulation, forinstance, or may be applied to an object to be coated.

Still further, the liquid may be atomized by using the energy of thecompressed gas to obtain a double-fluid spray.

Furthermore, in the present invention, the liquid can be sprayedintermittently (discontinuously) at a rate of 30 to 3,600 pulses perminutes or higher if conditions are met in order to maintain the amountof the liquid dispensed per unit time accurately. This operation can beeasily carried out by activating the piston 2 intermittently by openingand closing the three-way solenoid valve 12 for compressed air, which isconnected to the auto dispensing valve 1, intermittently with an unshowncontroller or the like. It has been generally impossible to continuouslyspray the liquid including solid particles at an extremely low flow rateof about 1×10⁻⁶ m³ to 10×10⁻⁶ m³/minute (about 1 cc to 10 cc/min)because the space between the nozzle or the needle 3 and the valve seat4 could not be made small due to occlusion by agglomerates of the solidparticles. By combining the method shown in JP-A 61-161175 proposed bythe inventors of the present invention with the present invention, thedispersion state of the solid particles can be stabilized at any time,thereby making it possible to perform high-quality spray.

FIG. 2 shows a liquid dispensing method and apparatus according to theliquid moving method according to another embodiment of the presentinvention.

A liquid 26 pressurized and filled in a vessel 21 is pumped to a vessel23 through an auto-dispensing valve 22 connected to a pipe 27 as a flowpassage while its flow rate is regulated by flow rate regulating meanssuch as an unshown orifice. The liquid accumulated in the vessel 23 ispumped to the vessel 21 through a pipe 28 by an inexpensive pump 24 at ahigher liquid pressure to be circulated. The pump 24 is a commerciallyavailable inexpensive pump such as a diaphragm pump or tube pump whichcan maintain pressure applied to the liquid in the vessel 21 at a fixedlevel by using a regulator with relief 25 for compressed gas or the likeeven when there are irregular pulses or the level of the liquid in thevessel 21 rises. In addition, the pipe 28 for connecting the pump 24 andthe vessel 21 may be provided with a check valve therebetween ifnecessary. Even when this method for moving the liquid is employed, theliquid having high quality and uniform dispersibility of particles isdispensed by the auto dispensing valve 22 for a desired period of time,thereby making it possible to perform smooth continuous operation.

FIG. 3 and FIG. 4 show a liquid dispensing method and apparatusaccording to still another embodiment of the present invention. FIG. 3is a system diagram of a liquid dispensing apparatus having threevessels and FIG. 4 is a time chart showing the three vessels of theliquid dispensing apparatus shown in FIG. 3 illustrating in time seriesthe relationship among flows of the liquid from the respective vessels.

An air regulator 35-1 for supplying a compressed gas is connected to avessel 31-1 through a three-way solenoid valve 36-1. The solenoid valve36-1 is in an open state by an instruction from an unshown controllerincorporated with a program and installed separately. A liquid 34 in thevessel 31-1 is pressurized by the pressure of a compressed gas whosepressure has been adjusted by the regulator set to a desired pressure toflow into a flow passage 37 and passes through an on-off valve with anorifice 32-1 which is at an open position by an instruction from thecontroller and further through an auto dispensing valve 33 and an on-offvalve with an orifice 32-3 which is in an open state and connected to avessel 31-3, to move into the vessel 31-3. The vessel 31-3 is connectedto an air regulator 35-3 for adjusting the pressure of a compressed gasthrough a three-way solenoid valve 36-3 which has already beeninstructed to be closed and is at a position where the inside of thevessel 31-3 communicates with an air opening port.

Further, a liquid accumulated in a vessel 31-2 does not move because anon-off valve 32-2 instructed to be closed but pressurized with acompressed gas because a solenoid valve 36-2 connected to the vessel31-2 is instructed to be opened. When the liquid in the vessel 31-1reaches a lower limit, an unshown liquid level sensor or the likedetects this and an opening instruction is given from the controller tothe on-off valve 32-2 connected to the vessel 31-2 so as to start movingthe liquid in the vessel 31-2 to the vessel 31-3. For example, theon-off valve 32-1 which receives an instruction from the controllerafter 20 milliseconds is closed and the solenoid valve 36-1 is alsoinstructed to be closed at the same time, so that the air opening portof the solenoid valve 36-1 is connected to the inside of the valve 31-1to reduce the inside pressure of the valve 31-1 to atmospheric pressure.

When the liquid level of the vessel 31-3 reaches an upper limit, theon-off valve 32-1 of the vessel 31-1 is opened upon detection by a levelsensor or the like connected to the controller to make the liquid alsoflow in the vessel 31-2 toward the vessel 31-1. At the same time, theon-off valve 32-3 connected to the vessel 31-3 is closed and thesolenoid valve 36-3 is opened for standby for the next switching.

This operation is performed periodically and the liquid can be dispensedat a desired timing during this operation. That is, during theabove-mentioned operation, the liquid including solid particles flowingthrough the flow passage 37 is dispensed by the liquid dispensing valve33 having the same constitution as shown in FIG. 1. Since the liquid ispumped in the flow passage 37 at this point, the precipitation of thesolid particles is prevented and the flow rate of the liquid is adjustedby the function of the orifices of the on-off valves with an orifice32-1, 32-2 and 32-3 so as to make the liquid flow in the flow passage ata predetermined rate. As a result, the liquid having high quality anduniform dispersibility of the particles is dispensed by theauto-dispensing valve 1 for a desired period of time so that smoothcontinuous operation is carried out.

Further, in the above-mentioned embodiments, the amount of the liquidequal to the dispensed amount can, always or regularly, be automaticallysupplied into a vessel or connection circuit by a liquid feeder.Further, in the present invention, the liquid is moved without stoppingthe pressurization of the liquid by pre-programming the controller basedon one dispensation without using a level sensor or the like, therebymaking it possible to dispense the liquid including solid particleswithout precipitating the solid particles and automatically replenishthe liquid.

In the above-mentioned embodiments, the number of vessels filled withthe liquid is 2 or 3. However, in the present invention, four or morevessels may be provided to carry out a desired combination of inflow andoutflow systems of the liquid through flow passages connecting thesevessels in order to dispense the liquid from the flow passages throughthe liquid dispensing valve.

As obvious from the above description, according to the presentinvention, there can be obtained a method and apparatus for dispensing aliquid, which make it possible to handle a minimum amount of the liquidwithout wasting it and to dispense or spray an exact amount of theliquid without precipitating the solid particles. That is, since theliquid including solid particles is pumped through a flow passage, theprecipitation of the solid particles is prevented and the flow rate ofthe liquid is regulated by the function of flow rate regulating means tomake the liquid flow through the flow passage at a predetermined rate.As a result, the liquid having high quality and uniform dispersibilityof particles is dispensed by a liquid dispensing valve for a desiredperiod of time, so that smooth continuous operation can be carried out.Therefore, the invention is particularly useful when the vessel is asmall-sized vessel and an expensive liquid is filled in the vessel to bedispensed from the vessel, because a minimum and exact amount of theliquid can be dispensed without wasting it.

1. A liquid dispensing apparatus comprising: a first vessel configuredto be filled with a liquid; a second vessel configured to be filled withthe liquid; a flow passage connecting said first and second vessels, theflow passage constructed and arranged to enable the liquid to flowbetween the first and second vessels; a valve coupled with the flowpassage, the valve configured for dispensing the liquid from the flowpassage; a first pressurizing device configured to apply a firstpressure to the liquid in the first vessel; a second pressurizing deviceconfigured to set a second pressure of the liquid in the second vessel;and a first flow rate restricting member disposed in the flow passage;and a second flow rate restricting member disposed in the flow passage;wherein the first and second flow rate restricting member are configuredto regulate a flow rate of the liquid flowing in the flow passagebetween the first and second vessels when the first and secondpressuring devices are operated such that the first pressure applied tothe liquid in the first vessel differs from the second pressure appliedto the liquid in the second vessel.
 2. The apparatus of claim 1 whereinthe first and second pressurizing devices each use compressed gas toapply the first and second pressures.
 3. The apparatus of claim 2wherein the compressed gas is applied using a plunger provided betweenthe compressed gas and the liquid.
 4. The apparatus of claim 1 whereinthe valve includes a spray nozzle.
 5. The apparatus of claim 4 whereinthe spray nozzle atomizes the liquid using a gas.
 6. The apparatus ofclaim 1 wherein the first flow restricting member includes an orifice.7. The apparatus of claim 6 wherein the second flow restricting memberincludes an orifice.
 8. The apparatus of claim 1 wherein the first andsecond vessels are syringes.
 9. The apparatus of claim 1 wherein thefirst flow restricting member is disposed in the flow passage betweenthe valve and the first vessel.
 10. The apparatus of claim 1 wherein thesecond flow restricting member is disposed between the valve and thesecond vessel.